Synthetic filaments produced from thermoplastic polymers have long been used as an alternative for natural bristles such as hog hair in the manufacture of paintbrushes. These thermoplastic polymers provide advantages over natural bristles in cost, consistency of quality, and performance, especially in modem day paintbrushes as painting has transitioned from solvent based to water based. The thermoplastic filaments are often tapered to provide a large diameter end (butt) which is contained within the ferrule of the brush while providing a smaller diameter end (tip) at the end of the paintbrush. A typical paintbrush, as shown in FIG. 3, has a handle 2, a ferrule 4, and bristles 6.
The synthetic filaments can be produced from a wide variety of thermoplastic polymers including polyamides, polyesters (U.S. Pat. No. 3,706,111), and polyolefins, in a wide variety of configurations including solid and hollow, and in a wide variety of cross-sections, including circular, oval, trilocular, tetralocular, lobate (U.S. Pat. Nos. 4,279,053 and 4376,746, Can. Pat. No. 1,007,032), or may contain multiple voids. Much work has been done in the trade to improve paint pickup and paint release of paintbrushes by experimenting with blends of different polymers, configurations, and cross-sections. However, with all the inventions in these areas introduced to the trade in the past, the highest quality, best performing, professional brushes of today are still produced from tapered solid round filaments of nylon 6,12 (specifically filaments sold under the trademark TYNEX.RTM. filaments by E. I. du Pont de Nemours and Company) blended with tapered solid round filaments of polybutylene terephthalate (specifically filaments sold under the trademark OREL.RTM. filaments by E. I. du Pont de Nemours and Company).
U.S. Pat. No. 5,032,456 teaches a microcellular filament to better simulate the surface of natural hog bristle for paint application. This filament has a porous surface to improve paint pickup and hold, but does not show any improvement in paint release. Also, because of these pores on the surface, brushes made with these filaments can be hard to clean, and as a result, these filaments are not used in premium professional brushes today. In U.S. Pat. No. 5,128,208, improved paint pickup in oil paints is accomplished by a filament that is easily flagged. However, this filament is not preferred because it is difficult to tip without flagging and does not provide any improvement in paint release, especially of water based paints. U.S. Pat. No. 4,279,053 discloses trilocular and tetralocular filaments to provide improved flagging and lower filament densities. Although the improved flagging accomplished with these filaments can improve the paint pickup of the brush, the trilocular filaments do not have the required stiffness and bend recovery that allow for use in premium professional brushes.
Significant work has been done in the past to add clay or silica of various sizes and of various amounts to nylon and polyester filaments and fibers to improve physical properties such as strength, fracture toughness, or abrasiveness. E. I. du Pont de Nemours and Company sells an abrasive filament, marketed under trade name TYNEX.RTM. A, which contains aluminum silicate, but is not tapered, and is not used in or recommended for use in paintbrushes. U.S. Pat. No. 5,722,106 discloses the addition of clay to nylon and polyester level (non-tapered) filaments as a polishing agent for use in toothbrushes. But the disclosure does not consider pickup and release properties or the use of clay additives for tapered filaments for use in coating applications. Clay or silica has also been added to filaments and fibers to better imitate natural bristles in surface appearance and feel, but no work has been done where clay was added to tapered filaments for use in paintbrushes or other coating application uses. Furthermore, no tapered filament has shown the magnitude of improvement in paint pickup and release and paint stripe length as the filament of this invention.